The present embodiments relate to automatic recognition of at least one anatomical landmark in a hollow organ of a patient.
In general, a marking of anatomical landmarks in medical images is an important method of operation in order to prepare therapy planning, for example. One example from electrophysiology (EP) is the position of the pulmonary vein (PV) ostia and of the left atrial appendage (LAA) in a left atrium. The marking of the pulmonary vein ostia makes it easier to navigate catheters, since a position of the pulmonary vein ostia may be used for the automatic planning of catheter ablations (Koch et al., Automatic planning of atrial fibrillation ablation lines using landmark-constrained nonrigid registration, J. Med. Imag. 1(1), 2014), and since the form of the pulmonary vein ostia is an important criterion in relation to the choice of the cryo-balloon catheter to be used. A marking of the regions and a display in an x-ray overlay image is important for avoiding injuries caused by incorrect introduction of the catheter.
Other examples from EP are the detection of common ostia and the detection of the additional pulmonary veins (fifth PV). Other applications of the proposed method are found, for example, in the field of structural heart disease. In this field, the determination of diameters is important (e.g., for valve replacement, for the aorta valve), since the choice of size and possibly also type of valve may be made accordingly. The method may likewise be used for the detection of drainages. A further field of application is the field of abdominal aorta aneurysms (e.g., the choice of the appropriate stents). Additional applications are to be found in the detection of stenoses in blood vessels and airways as well as in the detection of fluctuations of the diameter (e.g., expansions and constrictions) in the gastro-intestinal tract.
For therapy planning, it is usual to mark important anatomical landmarks because anatomical landmarks are critical and may not be constricted under any circumstances (e.g., liver arteries in AAA therapies, coronary arteries in aorta valve positioning, LAA for EP ablation with atrial fibrillation) or because the anatomical landmarks are important for the positioning of devices (EP pulmonary vein isolation). In EP in general, the model of the left atrium is segmented using an automatic segmentation tool from a 3D CT or MRI volume. The 3D model (e.g., shown as a mesh) is then displayed to the observer in an interactive 3D view. The user marks a series of points on the surface of the mesh to create a marking of the PV ostium and of the LAA. Thereafter, the marked model is visualized as part of an x-ray overlay image, through which the x-ray overlay image may then be used to simplify the navigation within the 3D chamber.
As an alternative, a statistical model of the outline may be used for the segmentation, with the model containing the body of the LA and the pulmonary veins modeled individually in each case. On account of the structure of the model, the marking of the pulmonary vein ostia may be derived implicitly from the transition from LA body to the pulmonary veins (e.g., from the article by Karim et al., Left atrium pulmonary veins: segmentation and quantification for planning atrial fibrillation ablation, Proc. SPIE, 2009, p. 72611T ff. or from the article by Zheng et al., Precise segmentation of the left atrium in C-arm CT volumes with applications to atrial fibrillation, Proc. IEEE Int. Symp. Biomed. Imaging, IEEE, p. 1421 ff., 2012). As an alternative, a semi-automatic approach may also be used (Rettmann et al., Identification of the left pulmonary vein ostia using centerline tracking, Proc. SPIE., Vol. 7262, p. 726228ff., 2009). This method provides that the user clicks manually on each of the four pulmonary veins in order to calculate a centerline (e.g., three-dimensional (3D) central line). For each point of the centerline, the region of the intersection of the pulmonary veins will be calculated, and the first point, as from which the region of the intersection becomes significantly larger, will be considered as the ostium.